1. Field of the Invention
This invention concerns improvements in and relating to investigating corrosion, particularly but not exclusively in relation to investigating corrosion in already corroded materials using field signature method based investigations.
2. Present State of the Art
The field signature method is based upon feeding a direct current through a location and measuring the electric field which is generated as a result using an array of electrical contacts on a surface of the location. Changes in the magnitude and shape of the electric field over time can provide significant information on corrosion occurring at the location.
To make measurements, an excitation current has to be applied to the location. The voltage across one or more pairs of contacts on the location to be measured and the voltage across one or more pairs of contacts on a non-corroding reference are measured repeatedly to monitor the corrosion that might be occurring.
Such techniques are known for monitoring future corrosion of new components. Generally speaking a pipeline to be monitored is installed and during its installation field signature measuring apparatus is provided for one or more short lengths of the pipeline. The electrodes used to measure the voltage are welded onto the surface of the pipeline to provide long monitoring lifetimes. Immediately on installation measurements are taken to establish the uncorroded voltage values for the various electrodes. These measurements form the base line values for subsequent measurements over the months and years as corrosion progresses.
Field signature methods to date are only available when provided with the location to be investigated when it is new and/or on the basis that any pre-existing corrosion is ignored and remains unquantified.